Joe Bonanno is the one who first told this story. According to him,Gambino was "a squirrel of a man,a servile and cringing individual". He states that he once saw Albert(Anastasia) get so mad at Carlo for bungling an errand that he raised his hand and almost slapped him,but didn't actually make contact.

Bear in mind that when this incident allegedly occurred,Anastasia was the Boss of the Family,and Gambino's superior,so he could have feasibly done it without any repercussions.